Won't the reefs migrate northward over time? If the water temperature off Hilton Head will be about the same in 100 years as it is now in the Florida Keys, why wouldn't coral get a foothold there? It may take a while, but I don't think reefs are going to go extinct.
-ccm
For coral reefs, that's taking the long view. Remember that habitats like the Bahamas resulted from climate processes that occurred over the past 400,000 years or so. While there could be some migration, they have to have someplace to go. And coral reefs don't just get up and walk. Plus, in addition to warming, increasing CO2 from the atmosphere acidifies the oceans, making it harder for the organisms to make the limestone (CaCO3) that forms the reefs. So there are significant difficulties ahead for reefs this century.